In some types of packaging material, paper, paperboard and other types of cellulose-based webs (collectively referred to herein as "paper") are provided with a smooth white surface, e.g., with a clay-titanium dioxide-latex mixture, in order to permit decoration of the naturally brown, rough surface of the underlying cellulosic material. In some cases, a white outer surface is provided through the lamination of an outer thin plastic layer which increases the tear strength of the underlying cellulosic web. See, for example, U.S. Pat. No. 4,254,173, the contents of which are incorporated by reference herein.
A problem which affects the appearance, and ultimately the economics, of laminations of thin plastic films to paper is the show-through or transmittance of the surface texture of the paper surface through the relatively thin polymer film. The result is that comparatively expensive coated grades of paper are used to project a smooth surface rather than less expensive uncoated, rougher surfaced sheets.
U.S. Pat. No. 4,377,616, the contents of which are incorporated by reference herein, discloses an opaque biaxially oriented polymer film structure comprising a thermoplastic polymer matrix core layer possessing numerous voids, a substantial number of which contain at least one spherical void-initiating particle, and transparent skin layers adhering to the surfaces of the core layer. The unique structure of the core layer imparts a much higher degree of opacity, possibly due to the effects of light scattering, than that possible by the use of opacifying pigment alone. There is no disclosure or suggestion in U.S. Pat. No. 4,377,616, however, of laminating the film structure disclosed therein to paper or other web, either directly or indirectly through an intermediate polymer foam layer. Although U.S. Pat. No. 3,676,242 discloses a laminate of a melt-blown non-woven mat and a polyolefin film, there is no suggestion of employing a film layer possessing anything like the lustrous, opaque appearance polymer film structure of aforesaid U.S. Pat. No. 4,377,616. Laminates of thermoplastic polymer foams and kraft paper are known from U.S. Pat. No. 4,180,427.